1. Field of the Invention
The present invention is directed to a system and method for electronically controlling the refrigeration and/or heating of the product storage compartment in a vending apparatus.
2. Related Art
Currently, vending machines have widespread application and utilization. Vending machines can be found not only in restaurants and other eateries, but also both inside and outside such facilities as offices, recreation centers, hospitals, gasoline stations, and apartment complexes. Because of their location, vending machines often experience both high and low levels of usage over a period of time. Further, such machines may be exposed to extremes of temperature and humidity for extended periods. Some vending machines are run for so long that ice and frost occur in the machines even though the products to be dispensed are warm.
When a vending machine is exposed to extremely cold temperatures, its cooling system should not be running continuously. In fact, prolonged periods of cold weather can freeze the products in the vending machine.
Moreover, when a vending machine door is open for loading or servicing, continuing to run the machine""s compressor may cause problems in normal operation.
In the prior art, various types of systems have been proposed and implemented to optimize vending machine operation under varying conditions. For example, U.S. Pat. No. 5,231,844 to Park discloses a refrigerator defrost control method in which the refrigerator is defrosted by comparing a sensor temperature in the refrigerator with a predetermined temperature during a defrost period. This defrost control method includes sensing the open/closed conditions of the refrigerator doors, and activating a defrost heater when the doors are closed.
U.S. Pat. No. 5,228,300 to Shim discloses an automatic refrigerator operation control method that includes controlling the temperature setting of a chamber; defrost cycling; and the operation of a compressor and fan motor according to the frequency of the door being opened and closed and to the open time of the door.
U.S. Pat. No. 5,046,324 to Otoh, et al. shows a defrosting controller for refrigeration systems. The controller determines a frost melting period from the measurements of the evaporator temperature during defrosting by means of an evaporator temperature sensor.
U.S. Pat. No. 4,932,217 to Meyer shows a process for controlling a heater; particularly, a defrost heater for refrigeration plants. In this process, the temperature of the room to be heated is measured at intervals of time and in each case a measured temperature value is stored.
U.S. Pat. No. 4,916,912 to Levine, et al. shows a heat pump with adaptive frost determination functions.
U.S. Pat. No. 4,903,501 to Harl discloses a refrigerator air-control heated baffle.
U.S. Pat. No. 4,850,198 to Helt, et al. discloses a refrigerator compressor control method involving momentarily energizing the compressor after extended off periods.
U.S. Pat. No. 4,745,629 to Essig, et al. discloses an improved duty-cycle timer that provides a duty-cycle control signal having alternate xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d intervals of different logic states. In one embodiment of this invention, the duty-cycle timer controls operation of a refrigeration circuit defrost mechanism.
U.S. Pat. No. 3,518,841 to West, Jr. discloses a household refrigerator apparatus that includes an evaporator automatically defrostable through use of an electric heating element energized at varying timed intervals.
In comparison to the present invention, devices and systems known in the prior art, such as those discussed above, do not directly address or solve the problems to which the present invention is directed but rather suffer from those same problems and disadvantages. In particular, conventional refrigeration control systems suffer from unnecessary compressor cycling when the refrigeration system attempts to start before pressures have equalized in the evaporator and the condenser. Also, conventional control systems do not effectively maintain refrigerated compartment temperature when outside temperatures are extremely cold for extended periods. Instead, such systems remain unnecessarily idle, with the compressor off, for periods in excess of several hours, thereby allowing ambient conditions to determine the refrigerated compartment temperature. Even further, the conventional refrigeration control systems in the prior art do not provide service personnel any way to efficiently troubleshoot the vending machines.
One main object of the present invention is to provide a system and method for efficiently controlling the refrigeration system (i.e., the compressor and its related components) and heating element of a vending machine. In particular, a specific object of the present invention is to provide a system and method of controlling a vending machine so as to prevent both unnecessary cycling of the compressor and ineffective maintenance of the refrigerated compartment temperature under extreme operating conditions. The present invention includes specific features that are lacking in the teachings of the prior art.
The features of the present invention include the ability to activate a timed defrost mode with no heating or cooling activity, and the ability to use an electric heater to prevent products in the vending machine from freezing when outside temperatures are extremely low. Further, the present invention includes a logic test with temperature sensing to determine both ambient conditions and controlled cabinet temperature.
Another object of the present invention is to provide an electronic control system that allows service personnel to efficiently troubleshoot problems in the vending machine. In particular, the system provides service personnel an electronic memory that stores information on error conditions and a display for showing the cabinet temperature at the sensor location.
Overall, a main object of the present invention is to provide a system and method for controlling the temperature of a vending machine more efficiently and reliably.